Luminaires based on red, green, and blue (RGB) light-emitting diodes (LEDs) generate various colors of light, which produce white or colored light when properly combined. RGB LED luminaires are used, for example, in LCD back-lighting, commercial-freezer lighting, and white light illumination.
Usually, for these multi-color LED-based luminaires, the controller of the light engine receives from a user or a higher level system, e.g. a building management system, the desired or targeted color point and light level. These setting values can be specified with tristimulus values in CIE x, y, L representing a certain position in the CIE 1931 chromaticity diagram created by the Commission Internationale de l'Eclairage (CIE), and thus need to be transformed into duty cycles or power levels for each connected LED color. Then, the transformation can be individually performed by a distribution of LED controllers through a calibration matrix (inverted C-matrix) shared between all of them.
However, illumination by means of such LED-based luminaires presents difficulties because the optical and electrical properties of individual LEDs vary with temperature, forward current, aging and manufacturing process. In particular, change in temperature of the LED p-n junction leads to changes in light flux output and peak wavelength of the LED, such that the calculations through the calibration matrix are also temperature dependent.
Additionally, it can be possible that no entity inside the light engine has a gamut knowledge. Under these circumstances, these variations can hence lead to abnormal situations for which the light engine cannot render the targeted color point and light level externally input by the user or the higher level system. Examples of such abnormal situations can be non-existing color points, e.g. (0,1), (1,0), (0.05,0.1), or color points outside the color gamut of the light engine due for example to multiple luminaires connected to the same communication databus controlled by the light engine, requiring thereby negative power levels for some LED colors, or light levels at a color point beyond the capabilities of the light engine, requiring thereby power levels beyond the capabilities of the corresponding LED colors.
In normal situations, each LED controller can perform the aforementioned calculations independently of the other since a single row of the calibration matrix is needed. However, in abnormal situations such as described herein, the LED controllers are required to communicate between them through the parameters of the calibration matrix to achieve a logical behavior. But this is not always possible according to the architecture of the light engine.